I can't install an anti-virus?

Oi computer experts please help!! Basically I want to install AVG Free on a computer, but there are still remnants of a previously uninstalled program called Trend Micro Security... And everytime I try to uninstall Trend Micro Security, I can't uninstall it, the uninstall program fails.. As some files are missing i think? Anyway is there a way i can permanently delete this program from my computer without uninstalling? Or are there other ways... Every time I try to install AVG Free... it's interrupted because it detects Trend micro... HELP PLEASE Thanks.